Telephone system



Dec. 12, 1939. Rlc ARDs 2,183,030

TELEPHONE SYSTEM Filed June 14, 1937 2 Sheets-Sheet 1 IN VE N TOR lDR/STREVOR R/CHA RDS ATTY Dec. 12, 1939. l. T. RICHARDS TELEPHONE SYSTEMFiled June 14, 1937 2 Sheets-Sheet 2 IN VE NTOR vop R/CHARDS- I IDPISTRE Z ATTY Patented Dec. 12, 1939 lTED srAres- PATENT OFFiCE signor toAssociated Telephone & Telegraph Company, Chicago, 11., a corporation ofDelaware Application June 14,.1937,.Serial'No. 148,013 In GreatBritain-July 21, 1936 '7 Claims.

The present invention relates to automatic switches for use in automatictelephone or like signalling systems and while more particularlyconcerned with the provision of additional facilities on group selectorswitches, the invention is also applicable to final selector switchesand other switches responsive to series of impulses.

Arrangements have already been made in which a group selector has accessto either of two sets or groups of outlets. After stepping the switchvertically to particular levels the switch is caused to release therebyabsorbing the first digit whilst at the same time outgoing leads in theswitch are changed over to a second set of wipers so that afterreceiving the second digit the switch again steps vertically and thenhunts automatically in a rotary direction for afree outlet in a group ofthe second set. Should the first digit dialled step the switch to anyother level the switch will hunt automatically for a free outlet in agroup of the p first set only.

According to one feature of the invention a switch having access to twodifferent sets of lines is provided with circuit arrangements whichcause access to be had to a line of one set'in response to one or moreseries of impulses of a predetermined number or numbers respectively andalso in response to a series of impulses of another predetermined numberdifferent from that of the 30 first of these series followed by theaforementioned one or more series of impulses and cause access to be hadto a line of the other set in response to a series of impulses of afurther predetermined number difierent again from said 35 otherpredetermined number followed by one or more further series of impulses.

According to another feature of the invention a switch having access totwo different sets of lines is provided with circuit arrangements whichcause access to be had to a line of one set in response to two series ofimpulses of predetermined numbers and also in response to a series ofimpulses of a diiferent predetermined number from the first of theseseries followed by two further series 45 of impulses corresponding tothe aforesaid numbers and cause access to be had to a line of the otherset in response to a series ofimpulses of a third predetermined number'difierent again from said different predetermined number fol- 50 lowedby two further series of impulses.

According to a further feature of the inven-- tion a group selectorswitch having access to two sets of groups of lines is provided withcircuit arrangements which in response to a series of im- 55 pulses of apredetermined value or values cause values followed by a second seriesof impulses cause the switch to hunt for an idle line in a group of theother set.

The invention will be better understood from p the following descriptionof one method of carrying it into effect, reference being had to theaccompanying drawings which illustrate the circuitsof a group selectorand comprise Figs. 1 and 2 which should be arranged side by side to forma complete circuit diagram. The diagram shows a circuit employing aswitch of the twodirectional type arranged to have so-called rectangularmotion.

For the purpose of the description it will be assumed that on dialling'7 as a first digit the switch performs a digit absorbing and wiperswitching function while on dialling 5 as a first digit the switchperforms a digit absorbing function only, while on other digits theswitch functions as an ordinary group selector.

When the calling subscribers loop is extended across the incomingnegative and positive conductors by way of a line finder or othernonnumerical switch relay A operates over its outer windings in seriesandat armature at operates relay B. Armature bl thereupon extends aguard earth on the incoming P conductor, armature b2 completes a lockingcircuit for relay B, armature bl completes a circuit to light thesupervisory lamp LP which is connected to battery over common conductorI!) by way of equipment which is arranged to give an alarm if the switchfails to step oifnormal and open springs N2 within apredetermined periodwhile armature b5 com pletes an operating circuit for relay C on itslefthand winding by way of resistance YD, contacts 5 NPAI, armatures b5-and b2, magnet VM (nonoperative in this condition) to battery. If theswitch is functioning as a first selector the middle winding of relay Ais connected to earth at armature b3 by way of a dial tone transformerover common conductor I2 so that dial tone is applied. to the incomingspeaking leads in a balanced circuit by induction from the middlewinding of relay A to the two outer windings so as to inform the callingsubscriber that he may com- 5 mence dialling. Relay C in operating atarmature cl prepares a circuit for the vertical magnet VM which howeveris non-operative in series with the winding of relay B.

When the first series of impulses is received relay A responds and eachtime it releases a circuit is completed to energise the magnet VM asfollows: earth, armature b2, resting armature ai, low resistancerighthand winding of relay C in parallel with resistance YA, contactsNR4, armature ci, magnet VM to battery, and accordingly the switchwipers are raised to the level dialled. During the impulse train it willbe noticed that relay B is intermittently short-circuited by the restingarmature a! but this relay will remain held due to the slugging eifectof the short-circuited winding. The presence of the metal rectifier MBAin the energising circuit of relay B prevents the slowing down of thevertical magnet operation which would otherwise result by the directconnection of the comparatively low value non-inductive resistance YC inparallel with its winding. It will be readily understood that neitherthe vertical magnet nor relay C will hold in series with relay B andmoreover the inductance of the latter relay is such that it has noappreciable eifect on the performance of the magnet.

On the first vertical step the off normal springs N are mechanicallyoperated and at contacts N2 the supervisory lamp LP is extinguishedwhilst at contacts N4 an operating circuit for relay H is completed onits lefthand winding. Armature hi thereupon connects the righthandwinding of relay H to the test wiper Pl, armature 71.2 disconnects theenergising circuit of relay C over its lefthand winding while armature723 extends an earth to short-circuit this winding and the sluggingeiiect thus produced enables relay C to hold satisfactorily during thetrain of impulses received.

Assuming now that any digit except 5 or '7 has been dialled, at the endof the impulse train relay A remains steadily operated and holds relayB. After a short interval relay C releases and completes an energisingcircuit for the rotary magnet RM from earth, armature h5, rotary magnetinterrupter contacts rm, off normal contacts N i, armature c3 and themagnet RM to battery whereupon the wipers are advanced into engagementwith the first set of contacts in the level selected. The rotary oifnormal springs NR are mechanically operated on the first rotary step andat contacts NR4 disconnect the vertical magnet W from the impulsingcircuit to prevent any further actuation. On energisation of the magnetthe rotary interrupter contacts rm are opened also.

If the test wiper Pl encounters an engaged outlet which is indicated byan earth or booster battery potential, relay H will be held operatedover armature dr2, contacts NPBI armature dafi, contacts Si and armaturehi on its right hand winding and the disconnection of its originalholding circuit by the interrupter contacts rm is therefore withouteiiect. However the rotary magnet RM is de-energised and on closure ofthe interrupter contacts the magnet is re-energised to advance thewipers on to the second set of contacts. This stepping operationcontinues automatically until an idle outlet in a group of the first setof lines is found or alternatively the wipers are advanced to the 11thposition.

If the Pi wiper encounters a free outlet, that is, one unmarked by earthor booster battery p0- tential, relay H will quickly restore and atarmature h5 opens the magnet driving circuit while the selected outletis immediately busied from earth, armatures bl, h and dafi, contactsNPBi, armature (U2 and the Pi wiper. A circuit is now completed tore-energise relay C on its lefthand winding in series with resistanceYD, contacts NPAl, armatures b6 and 712 and the vertical magnet tobattery and this relay in operating at armatures c5 and c6 switches theincoming speaking leads through resting armatures dad and (Z to thefirst choice negative and positive wipers. Armature c3 disconnects anycircuit to the rotary magnet and at the same time reoperates relay Hover its lefthand winding whereupon it holds on its other winding by wayof armatures hi and 04 to the carthed P conductor. Relay C in operatingat armatures c5 and 06 also releases relay A which in turn at armaturea! short-circuits and releases relay 3. Meanwhile, however, the loopextended over the negative and positive wipers operates the A and Brelays in the succeeding selector whereupon a guard earth is returnedover the P lead to maintain relay H when subsequently relay B releasesafter its slow release period. Relay B in releasing at armature b5disconnects the lefthand winding of relay H which remains held on itsrighthand high resistance winding to the earthed P lead.

On dialling the second and subsequent digits, trains of impulses areextended over the negative and positive leads to succeeding switches toroute the call to the wanted subscriber.

Assuming now that all outlets in the level selected prove busy thewipers are rotated to the 11th position where the cam springs S aremechanically operated. Since the P! wiper fails to encounter any earthpotential relay H will release quickly as described in the previousparagraph and open the driving circuit and re-operate relay C. Armaturesc5 and c5 switch the incoming leads as before through to the negativeand positive wipers which connect by way of the inultipled 11th stepcontacts to the outer windings of relay A. Relay A therefore remainsheld to the incoming loop and maintains relay B while relay H isre-operated at armature c3. Cam contacts S2 connect up the busy tonetransformer over common lead l3 to the middle winding of relay Awhereupon busy tone is induced in the outer windings and is applied in abalanced circuit to the incoming speaking leads. Cam contacts SI extendan earth over armature b1, contacts Si, armature daii, contacts NPB! andarmature drZ on to the test Wiper Pl to operate an overflow meter whichmay be connected to the 11th outlet of that particular level for trafiicobservation purposes.

Assuming now that '7 is dialled as a first digit thus raising the switchvertically to discriminating level, giving both wiper switching anddigit absorbing facilities, the normal post springs NPA are operated bythe switch shaft when the switch is set to the seventh level. At the endof the impulse train relay C releases after a short interval andcompletes an energising circuit for the rotary magnet at armature 03 inthe normal manner and as a result the wipers are advanced intoengagement with the contacts of the first outlet in the level selected.On this particular level the P contacts are left disconnected and sincethe Pi wiper picks up no potential relay H quickly releases and atarmature 71.5 disconnects the magnet driving circuit. It

should be stated here that this particular level 75 of outlets in thefirst setof lines irrthe particular of relay DR a circuit isalsocompleted from: earth; arrangement described cannot be utilised forrouting to succeeding selectors since it is. neoessary to disconnect thefirst P contactin order-to enable the switchto be released over the samepath as it has been set in a manner. tobe: de scribed. Relay H inreleasing-completes a'cir-' cuit to operate relay DR from: earth,lefthand winding of relay DR, armatures (1115 and da3; operated contactsN'PA-l, armatures b6 "and h2 and the vertical magnet to batterywhereupon armature dr3 extends an earth over off normal contacts NI,right hand low resistancewindingof relay DR which is shuntedby'resistance- YB for spark quench purposesand armatures b6 and 112 tooperate the vertical magnet VM. The vertical magnet pawl when operated.is arranged'to engage with an extension arm ofthe rotary detent and moveit out of engagement with the rotary ratchet member to initiate the fullrelease of the switch along. the path over which it has been set. Thisarrangement reduces the releasetime to a minimum and.enablesstheswitchtobe 7 This relay in operating at a make-first light armature da! looksover itsiother-windingtor the earthed P conductor, at armatureda23disconnects dial tone, and at armatures da4, 5 and 6 switches overthe negative, positiveand P leadsthrough to the second set of. wipers,i. e. the wipers having accessto the groups of lines of the second set.

Vi henthe switch commencesto release vertically the normal post springsrestore and when it releases completely the off normal. and: rotary offnormal springs will be restoredtov the. normal. condition. Contacts Nithereupon open.-thever-- tical magnet energising circuit and atthe-:same' time release relay DR since its'other" winding isdisconnected at armature daS:

R2, and the magnet VM to battery inorder to prepare the switch. forreceiving further dialled impulses.

On dialling the second digittheswitchsteps vertically and then performsan automatic rotary search for a free outlet in the manner described atthe commencement of the specification but in this case however thesearch takes place over contacts of lines of a group of the second setof outlets only. It will be noticed that any further operation of thenormal post springs N'PA or NPB is made inefi'ective at armatures da3and drzii and it will be appreciated that any digit from lfto 0 may thusbe dialled as a second digit.

Assuming now that 5 is dialled as a first digit the switch will beraised to the digit absorbing level whereupon the normal post springsNPA and NPB will be mechanically operated. At the end of the digit relayC releases after its slow release period and energises the rotary magnetwhich causes the switch to make one rotary step in the normal mannerwhereupon relay H quickly releases since a circuit tothe test wiper PIis disconnected at contacts NPBl. Relay H releasing opens the drivingcircuit and at armature 7L2 operates relay DR over its lefthand windingas before whereupon at armature 0373 the vertical magnet is energised inseries with the righthand Winding of relay DR. On operation Relay C. nowre-operates on its lefthand winding in series with resistance YD,contacts NPAl, armatures b6 and armature bl, M and dat; operatedcontacts NPBI and armature drl tooperate relay DB on its righthandwinding. This relay in operating at armature dbl locks to the earthed Pconductor, at armature ca /b3 prepares an alternative circuit to theNPBi contacts, at armature dba disconnects dial tone while at armaturedbS the lefthand winding of relay DB is disconnected. On energisation ofthe vertical magnet-as previously described the switch restores tonormal over the: path over whichit has been set-whereupon-aalllmechanically operated spring sets are restored to the normalcondition and atoifnormai contacts Nithe vertical magnet and'relay DRare released. A circuit isnow completed to= operate relay C over itslefthand winding inuthe normal manner in ordertoprepare for th'e seconddigit;

On reception of the second digit the switch steps vertically and huntsin a self-interrupted circuit for an idle line in a group-of the firstset. Since relay DB remains looked, any further operation ofthenormalpost springs will b'e ineifective and any digitexcept 7 maythus be dialled as a second digit;

On release of. the connection at the end of the conversation, earth isremoved from. the release trunk conductor P thus releasing relay: HI andeither relay DA or DB' whicheven-is operated and thereupon relay H inreleasing at armature ht disconnects the holding circuitfor relay C onits left-handwinding. On release of relayC- a selfinterrupted drivingcircuit is completed. for the rotary magnet RM from earth supplied tocommon conductor H by way of equipment which is arranged to' give adelayed: alarm in case of failure: to release; contacts N l; armaturect,ro-

tary magnet RM to 'eb'attery' and accordingly thewipers are rotatedclearof the'banks-after which they fall and rotate under the banks underspring tension back to their normal positions where the oil normalcontacts. N l open ancl disconnect the homing circuit. Preferablythe-rotary magnet is mechanically prevented fromopening its interruptercontactsduringthe release movement so that there is notendency'forit'to=chatter.-

At the commencement ofirelease an'initial unguard'period on the incomingPeonductor which is represented by the. sum of. the release timesofrelays H and C is provided to enable preceding switches to restore. Onrelease of relay C following the release of relay H earth will beextended by way of operated off normal contacts N3 and resting armature04 on to the P conductor to guard against premature seizure duringrelease. When the switch reaches normal, contacts N3 open and remove theguarding switch I thus freeing the switch from further use.-

A test buzzer connected to test jack T over common lead I l and armaturedal enables the set of wipers in use to be determined without removingthe dust cover from the switch.

It will be appreciated that while numerous facilities are oifered bythis switch, the number of levels which cannot be extended to succeedingswitches is reduced to a minimum. In the example described in thisspecification level i of the first set of groups of lines will be theonly level which cannot be utilised.

I claim:

1. In an automatic switch, a plurality of sets of wipers, means forcausing a connection to be extended over one of said sets of wipersresponsive to the receipt of impulses comprising a predetermined digitfollowed by impulses comprising any digit, and means for causing aconnection to be extended over another of said sets of wipers responsiveeither to the receipt of impulses comprising a predetermined digitdifferent from first said predetermined digit followed by impulsescomprising any digit except first said predetermined digit, or to thereceipt of impulses comprising any one of a plurality of predetermineddigits different from first said predetermined digit and second saidpredetermined digit. 7

2. In an automatic switch having access to the lines of each sub-groupof a plurality of groups of lines, means for operating said switch toextend a connection to an idle line of any desired sub-group of onegroup responsive to a train of impulses comprising a predetermined digitfollowed by a second train of impulses designating the desired subgroup,and means for operating said switch to extend a connection to an idleline of any desired sub-group of another group responsive either to atrain of impulses comprising a predetermined digit difierent from firstsaid predetermined digit followed by a second train of impulsesdesignating the desired sub-group or to a single train of impulsesdesignating only the desired sub-group.

3. In an automatic switch having access to a plurality of groups oflines, means for operating said switch to extend a connection to anyline of one of said groups responsive to the receipt of a train ofimpulses comprising a predetermined digit followed by a second train ofimpulses designating said one line, and means for operating said switchto extend a connection to any line of another of said groups responsiveeither to the receipt of a train of impulses comprising a predetermineddigit difierent from said first predetermined digit followed by a secondtrain of impulses designating last said line or to a single train ofimpulses designating only last said line.

secondary wipers having a normal position, a primary group of linesaccessible only to said primary wipers, a secondary group of linesaccessible only to said secondary Wipers, means for extending aconnection to any line of said primary group responsive either to asingle digit directed movement of said Wipers or to two digit directedmovements of said wipers wherein a predetermined first digit causes saidwipers to be returned to said normal position following the first ofsaid two movements, and means for extending a connection to any line ofsaid secondary group responsive only to two digit di rected movementswherein a predetermined first digit different from last said first digitcauses said wipers to be returned to said normal position following thefirst of said two movements and also causes said secondary wipers to beeffective.

6. In an automatic switch for absorbing certain digits, first-choicewipers and second-choice wipers having a normal position, a group oflines accessible to each set of wipers, means responsive to impulses formoving said wipers from said normal position, means effective if saidimpulses comprise any one of a plurality of predetermined digits forcausing said first-choice wipers to be effective in searching for anidle line designated by said one digit, means effective if said impulsescomprise a predetermined digit difierent from first said predetermineddigits for causing said wipers to be returned to said normal positionand for preparing for further impulse directed movement of said wipersin which said first-choice wipers will be effective, means effective ifsaid impulses comprise a predetermined digit difierent from first saidpredetermined digits and different also from second said predetermineddigit for causing said wipers to be returned to said normal position andfor preparing for further ill'lpulse directed movement of said wipers inwhich said second choice wipers will be effective.

'7. In an automatic switch as claimed in claim 6, wherein said thirdmeans and said fourth means also prevent a second return of said wipersto said normal position after said further impulse directed movement ofsaid wipers even though said further movement is responsive to impulsescomprising either of last two said predetermined digits.

IDRIS TREVOR RICHARDS.

